1. Technical Field
The invention relates to reinforced resilient pneumatic tires and more particularly to a vehicle tire reinforced by a thin annular composite band which enables the tire to run in an unpressurized condition and to provide greater puncture resistance for the tire. More particularly, the invention relates to a pneumatic tire in which the internal band element is formed to resist interlaminar shear stresses and provide enhanced inflated and uninflated banded tire durability and puncture resistance.
2. Background Information
Various tire constructions have been devised over the years which enable a tire to run in an under-inflated or non-inflated condition, such as after receiving a puncture and loss of pressurized air, for extended periods of time and at relatively high speeds. This enables the vehicle operator to safely drive the vehicle to an appropriate location for repair or replacement of the punctured tire. Certain of these safety tires, referred to as xe2x80x9crun flat tiresxe2x80x9d, have been successful for certain applications and certain types of tire constructions. Most of these run flat tires achieve their run flat capability, by the placement of reinforcing layers or members of relatively stiff elastomeric material in the side walls of the tire which enable the tire to support the vehicle weight even with the complete loss of internal air pressure. Examples of such prior art run flat tire constructions which use such sidewall inserts are shown in U.S. Pat. Nos. 3,911,987; 3,949,798; 3,954,131; 4,067,372; 4,202,393; 4,203,481; 4,261,405; 4,265,288; 4,287,924; 4,365,659; 4,917,164; and 4,929,684.
In addition to these prior art run flat tires, various run flat tire constructions have been developed which utilize a thin annular band which extends circumferentially throughout the tire beneath the tread area. Examples of such banded run flat tires are shown in the following patents.
U.S. Pat. 4,428,411 describes a method to make a particular band for use in a run flat tire which uses a series of side-by-side elements in the form a helix. The band has hoop compression as against a conventional breaker belt that has no significant compressive strength but is used only to resist tension loads endured by the tire when pressurized.
U.S. Pat. Nos. 4,673,014 and 4,794,966 teach a method to acquire desirable prestressing in a fabricated band made of helical elements. Physically bending the larger diameter helix element around a smaller mandrel and securing it with a resin impregnated tape acquires a desirable level of prestressing.
U.S. Pat. No. 4,456,048 teaches a method of acquiring a change in band stiffness as a function of deflection. The band has a lower stiffness for normal pressurized operation and has a higher stiffness to support load when the tire is uninflated and experiences larger deflection.
Japanese Patent application No. JP 63141809 discloses a run flat tire having a banded element which is formed of layered strips of materials, such as an arramed filament which is impregnated with a high elasticity epoxy resin, which after hardening provides a stiffened band. The tire of this disclosure requires that elastomeric side wall inserts be utilized in combination with the band in order to achieve the desired run flat characteristics.
Other run flat banded pneumatic tires are shown in U.S. Pat. Nos. 4,111,249; 4,318,434; 4,428,411; 4,459,167; and 4,734,144.
Banded tires have been fabricated with band materials made of steel, aluminum, titanium, and epoxy and thermoplastic composites with glass, KEVLAR (aromatic polyamide) and graphite fiber reinforcement. The common failure mode with such lightweight, economical laminate band constructions is interlaminar shear within the band""s primary bending neutral axis. This is a fatigue failure and is directly related to the spectrum of cyclic operating stress. As in all fatigue failures, the lower the stress, the longer the operating life. This problem of fatigue failure occurring along the neutral axis of the band resulting in interlaminar shear can be reduced by the prestressing the band during its manufacture, as described in U.S. Pat. No. 5,879,484.
Numerous prior art pneumatic tires have been provided with an annular band usually of metal, to resist puncture by sharp objects protruding through the tread area. Although these prior art puncture resistant tires utilizing a metal band provide the desired puncture resistance, in most cases, the metal band effects the ride characteristic of the tire and the life expectancy thereof.
Thus, it is desirable to provide a band element for run flat pneumatic tires and for pneumatic tires having greater puncture""s resistance, with increased resistance to interlaminar shear stress in the inflated deflected banded tire, the uninflated deflected banded tire and the condition of a banded tire encountering a road surface anomaly, which is accomplished without materially increasing the difficulty of the manufacturing process for producing the band element and without materially increasing the cost thereof. The band element of the present invention achieves these results.
Objectives of the invention include providing an improved pneumatic tire that is substantially similar in ride, comfort, durability and operation as conventional pneumatic tires, yet which is able to be operated safely at reasonable speeds and for a sufficient number of miles after loss of internal pressurization.
Another objective of the invention is providing such a pneumatic tire and band element therefor which has enhanced load carrying capability, improved endurance by minimizing band stress, and in particular minimizes interlaminar shear stresses heretofore resulting in destruction of the band element.
Another objective of the invention is to provide such a band element which has enhanced inflated durability achieved by increasing the interlaminar shear strength of the band by reducing circumferential strain and circumferential stress which is achieved by contouring of the band edges, and in which the enhanced durability is derived independent of other preferred band dimensions such as diameters, modulus of elasticity, prestressing of the band, etc.
A still further objective of the invention is to provide such a band element which reduces interlaminar shear by contouring of the band elements irrespective of whether the band element is fabricated of materials such as laminated metals, thermoplastic and thermosetting materials and multi-layer composites and is applicable to passenger tires, light truck tires, racing tires and tires with and/or without tread patterns.
Another objective of the invention is to provide such a run flat tire which has increased puncture resistance from the tread contacting road hazards, which can be manufactured at a cost and weight competitive with conventional non run flat tire constructions and which will permit the elimination of a spare tire conventionally required in automobiles thereby providing a cost saving to vehicle manufacturers and owners.
A further objective of the invention is to provide such a band element in which the interlaminar shear strength is increased by coating the tapered outer end portions with a graphite fiber filled epoxy resin.
These objectives and advantages are improved by a thin annular band for embedding in the crown portion of a pneumatic tire, said band having an axial width and a radial thickness with a neutral axis extending generally through the center of the band in an axial direction, said band being a composite member formed of a plurality of layers of an elongated strip material and having inner and outer annular axially extending surfaces terminating in a pair of outer end portions and a pair of end edges with certain of said end portions being tapered toward said pair of end edges.
These objectives and advantages are further obtained by a pneumatic tire having an elastomeric casing with a tread portion formed in a crown portion thereof and sidewalls extending from the crown portion to generally annular beads adapted to normally seat themselves in an air tight secured: relationship with a wheel; an annular band embedded in the crown portion having an axial width and a radial thickness with a neutral axis extending generally through the center of the band in an axial direction, said band being a composite member formed of a plurality of layers of elongated strip material and having inner and outer annular axially extending surfaces terminating in a pair of outer end portions and a pair of end edges with certain of said end portions being tapered toward said pair of end edges.